High temperature pressure sensitive adhesives

ABSTRACT

Novel silicone pressure sensitive adhesives containing relatively minor amounts of oil- or organic-metal salts are disclosed which exhibit improved high temperature stability properties.

This is a divisional of application Ser. No. 08/172,673 filed on Dec.22, 1993, now U.S. Pat. No. 5,491,811, which is a continuation ofapplication Ser. No. 07/895,297, filed on Jun. 8, 1992, now abandoned.

The present invention relates to pressure sensitive adhesivecompositions. More particularly, the present invention relates tosilicone pressure sensitive adhesives which exhibit excellent hightemperature stability. Most particularly, the present invention relatesto a silicone pressure sensitive adhesive composition containingrelatively minor amounts of oil or organic-soluble metal salts.

BACKGROUND OF THE INVENTION

The term "pressure sensitive adhesive" as used throughout the instantspecification refers to adhesives that can be adhered to a surface andyet can be stripped from the surface without transferring more thantrace quantities of adhesive to the surface, and can be re-adhered tothe same or another surface because the adhesive retains some or all ofits tack and adhesive strength.

Pressure sensitive adhesives of the prior art are generally of twogeneric types. The first type, organic pressure sensitive adhesives, areknown in the art to have the requisite physical properties and low costto make them suitable for a variety of applications. However, theorganic pressure sensitive adhesives have been found to be unsuitablefor applications requiring adhesion to low energy surfaces, improvedweatherability, high low temperature flexibility and good hightemperature stability. Thus, organic pressure sensitive adhesives havegenerally been found to be unsuitable for use in outdoor applicationssuch as outside graphics, automobile striping and for use in bondingplastics where temperature extremes are encountered.

The second type, silicone pressure sensitive adhesives, are also knownin the art and are employed in a wide variety of applications, such aspressure sensitive adhesive tapes. The silicone pressure sensitiveadhesives exhibit improved weatherability properties over the organicadhesives, such as exhibiting excellent adhesion to very low energysurfaces, flexibility at low temperatures and are chemically stable athigh temperatures.

Special mention is made of Traver, U.S. Pat. No. 5,096,981 whichdiscloses that less than 100 parts per million of certain metal saltscan be added to a pressure sensitive adhesive comprising a homogeneousmixture of two intermediate pressure sensitive adhesives.

The excellent properties of silicone pressure sensitive adhesives havecreated an increasing demand for still better adhesives which willwithstand the higher operating temperatures of modern equipment andprocesses. Thus, it would satisfy a long felt need in the art if asilicone pressure sensitive adhesive could be developed whichexhibited-still further improved high temperature stability over thesilicone pressure adhesives of the prior art.

To this end, the present invention provides a novel silicone pressuresensitive adhesive which exhibits improved high temperature stability,passing aging tests at temperatures above 550° F. Such novel siliconepressure sensitive adhesives and their improved high temperatureproperties are exemplified in the working examples of the presentinvention.

SUMMARY OF THE PRESENT INVENTION

According to the present invention there is provided a novel siliconepressure sensitive adhesive having improved high temperature stabilitycomprising:

(a) an aromatic hydrocarbon soluble resin copolymer comprising R₃SiO_(1/2) units and SiO_(4/2) units where each R individually representsa monovalent hydrocarbon radical containing no more than six carbonatoms and where the total number of R radicals having olefinicunsaturation is between 0 and 0.5 percent, there being from about 0.6 toabout 0.9 R₃ SiO_(1/2) units for every SiO_(4/2) unit;

(b) a hydroxyl, vinyl or hydride end-stopped diorganopolysiloxane; and

(c) more than 100 parts per million metal of oil- or organic-solublemetal salts based on the total silicone weight of (a) and (b).

Also according to the present invention there is provided a novel methodfor improving the high temperature stability of silicone adhesivescomprising (i) adding to a silicone adhesive comprising (a) an aromatichydrocarbon soluble resin copolymer comprising R₃ SiO_(1/2) units andSiO_(4/2) units where each R individually represents a monovalenthydrocarbon radical containing no more than six carbon atoms and wherethe total number of R radicals having olefinic unsaturation is between 0and 0.5 percent, there being from about 0.6 to about 0.9 R₃ SiO_(1/2)units for every SiO_(4/2) unit; and (b) a hydroxyl, vinyl or hydrideend-stopped diorganopolysiloxane; (ii) more than 100 parts per millionmetal of (c) oil- or organic-soluble metal salts based on the totalsilicone weight of (a) and (b).

Still further, the present invention provides articles of manufacturecomprising a silicone pressure sensitive adhesive comprising

(a) an aromatic hydrocarbon soluble resin copolymer comprising R₃SiO_(1/2) units and SiO_(4/2) units where each R individually representsa monovalent hydrocarbon radical containing no more than six carbonatoms and where the total number of R radicals having olefinicunsaturation is between 0 and 0.5 percent, there being from about 0.6 toabout 0.9 R₃ SiO_(1/2) units for every SiO_(4/2) unit;

(b) a hydroxyl, vinyl or hydride end-stopped diorganopolysiloxane; and

(c) more than 100 parts per million metal of oil- or organic-solublemetal salts based on the total silicone weight of (a) and (b).

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Silicone pressure sensitive adhesives are generally compositions whichare based on the combination of a resin (a) and a gum (b).

The resinous component (a) is preferably a resinous copolymer of the MQtype, i.e., comprising units derived from R₃ SiO_(1/2) (M units) andSiO_(4/2) (Q units). The R groups in the M units may be identical ordifferent and are monovalent hydrocarbon radicals containing no morethan six carbon atoms such as alkyl radicals, e.g., methyl, ethyl andisopropyl; cycloaliphatic radicals, e.g., cyclopentyl and cyclohexenyl;olefinic radicals, e.g., vinyl and allyl; and the phenyl radical. It ispreferred that at least 95 percent, and more preferably 100 percent, ofall the R radicals in the resinous copolymer are methyl and thatessentially all of the radicals are free of olefinic unsaturation. About0 to up to 0.5 percent of all R radicals in the copolymer can beolefinically unsaturated, such as with the vinyl radical. Morepreferably, the number of unsaturated R radicals can range from 0 to 0.2percent of all R radicals in the copolymer.

The Q units of the resinous copolymer are essentially all siloxaneunits, containing no silicon bonded carbon atoms and are derived fromthe silica hydrosol used in the preferred method of preparation asdescribed hereinbelow.

Resin copolymers (a) that are operable in the invention are soluble inaromatic hydrocarbon solvents such as benzene, toluene, xylene and thelike and have a ratio of M units to Q units of from 0.6:1.0 to 0.9:1.0.

The resinous copolymer (a) can be prepared by any of the known methodsfor preparing such resins. For example, cohydrolysis of an appropriateamount of each of the silanes of the formula R₃ SiX and SiX₄ to give Munits and Q units in the desired M:Q ratio in the resin copolymer can beused, where X is a hydrolyzable group such as alkoxy. Preferably, theresin copolymer is prepared by the method of Daudt et al., U.S. Pat. No.2,676,182. Briefly, the method of Daudt et al. comprises reacting underacidic conditions, a silica hydrosol with organo-substituted siloxanes,for example, hexamethyldisiloxane, or hydrolyzable organo-substitutedsilanes, for example, trimethylchlorosilane, or their mixtures andrecovering a resin copolymer having M and Q units which is soluble inaromatic hydrocarbon solvents.

The gum component (b) typically comprises a hydroxyl, vinyl or hydrideend-stopped polydiorganosiloxane. Particularly preferred are hydroxylend-stopped polydiorganosiloxanes having a viscosity of from about100,000 to about 500,000,000 centipoise, preferably from about20,000,000 to about 200,000,000 centipoise; and most preferably fromabout 40,000,000 to about 100,000,000 centipoise. The hydroxylend-stopped polydiorganosiloxanes useful in the practice of the presentinvention are generally represented by those of the general formula:##STR1## wherein each R¹ individually is a radical selected from thegroup consisting of alkyl radicals such as methyl, ethyl, propyl, hexyland octyl; alkenyl radicals such as vinyl, allyl, propenyl, butenyl andhexenyl; cyclic hydrocarbon radicals such as cyclohexyl andcyclohexenyl; and aryl radicals such as phenyl, 2-phenylethyl, tolyl andbenzyl. Methyl, vinyl and phenyl are, in general, the preferred R¹radicals, and the methyl radical preferably accounts for at least 50,more preferably 95, and most preferably 100 percent of all R¹ radicals.

A particularly useful polydiorganosiloxane fluid is a silanol-stoppedpolydimethylsiloxane fluid.

The polydiorganosiloxanes of the present invention can generally beprepared by any of the methods known in the art. For example, thepolydiorganosiloxanes can be prepared according to the method disclosedin U.S. Pat. No. 2,814,601 (Currie et al.), wherein an appropriatesiloxane is reacted with an aqueous acid in an closed system until theviscosity of the siloxane has become essentially constant. The productis then washed free of the acid.

Components (a) and (b) of the present invention may be combined in awide variety of proportions in preparing the silicone pressure sensitiveadhesives of the present invention. Typically, there is employedcomponent (a) in an amount ranging from about 80 to about 40 parts byweight and component (b) in an amount ranging from about 20 to about 60parts by weight based on 100 parts by weight of (a) and (b) together.More preferably, there is employed component (a) in an amount rangingfrom 80 to about 50 parts by weight and component (b) in an amountranging from about 20 to about 50 parts by weight based on 100 parts byweight of (a) and (b) together.

Essential to the practice of the present invention, the siliconepressure sensitive adhesives further comprise more than 100 parts permillion metal of oil- or organic-soluble metal salts based on the totalsilicone weight of (a) and (b). Addition of 100 parts per million metalor less of the metal salts do not yield the high temperature stablesilicone pressure sensitive adhesives of the present invention. Inpreferred embodiments, the amount of metal salt employed can range from110 parts per million metal to 2500 parts per million metal based ontotal silicone weight. Most preferred is where the silicone pressuresensitive adhesive of the present invention comprise component (c) in anamount ranging from about 200 to about 500 parts per million metal basedon the total silicone weight.

The metallic stabilizers (c) of the present invention can be added tothe pressure sensitive adhesives of the present invention in a varietyof forms, as long as they are oil- or organic-soluble, stable in thesilicone composition before use and are not prohibitive of siliconecuring.

Examples of suitable metals are the rare earth metals, e.g. lanthanum,cerium, praesodymium, neodymium, promethium, samarium, curopium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium andlutetium. Other useful metals are various transition metals, includingbut not limited to zirconium, titanium, nickel, iron, vanadium,chromium, maganese, cobalt, copper etc. Still other useful metals mayinclude magnesium, calcium, barium, aluminum and tin. It is alsocontemplated that combinations, i.e. blends, mixtures, complexes oralloys, of any of the above metals may also be employed. Typically, theoil or organic soluble metal salt compounds useful in the practice ofthe present invention comprise a rare earth metal salt of a carboxylicacid having from about 2 to about 18 carbon atoms. For example, thesecan include carboxylates, octoates, naphthenates, stearates andtallates. Preferred are compounds such as a rare earth metalcarboxylates, including but not limited to cerium 2-ethylhexanoate.

Metal carboxylates in organic solvents can be obtained commercially fromMooney Chemicals, e.g., or prepared by reacting the metal or metals ofchoice with carboxylic acid and diluted in a solvent such as mineralspirits. Also, other metal carboxylates can be prepared by reacting thedesired metal or metals with other carboxylic acids, such as aceticacid, propionic acid, 2-ethylhexonic acid, neodecanoic acid ornaphthenic acid.

Typically, the metal carboxylate salt used in the compositions of thepresent invention are in the form of a 20 percent to 65 percentsolution, of which from 6 to 8 percent comprises the active metal. Thevolatile solvents are primarily selected from the group consisting ofhydrocarbon solvents such as, e.g., mineral spirits, ether solvents suchas, e.g., diethylglycol monobutyl ether and 2-ethylhexoic acid. Examplesof other suitable solvents for metal carboxylate salts include, but arenot limited to, carboxylic acids of from 2 to about 18 carbon atoms,aliphatic hydrocarbon solvents such as hexane and heptane; aromatichydrocarbon solvents such as toluene and xylene; glycol ether; andketones.

The pressure sensitive adhesive of the present invention are generallyprepared by first mixing together components (a) and (b) in theirdesired proportions. This may be accomplished by any suitable means butin general it is preferable to employ a mutual solvent, such as anaromatic or aliphatic hydrocarbon solvent.

The rare earth metal salt is added slowly to the mixture of components(a) and (b) with agitation in order to get a good dispersion. Poordissolution or dispersion of the metal salts in the silicone compositioncan detract from the improved high temperature stability properties. Themixture is then blended until a uniform, homogeneous mixture is formed.They can be mixed using any of the techniques known to those skilled inthe art, such a milling, blending, stirring and the like, either inbatch or in continuous processes.

As soon as the ingredients are mixed, the composition is ready for useas a pressure-sensitive adhesive without further treatment. It is simplyapplied by any suitable means to the surfaces to be adhered, and thesurfaces are then brought together. If the adhesive is in solvent, it isbest to allow the solvent to evaporate before adhering the surfaces.

Application of the adhesive to the substrate surfaces can beaccomplished by a wide variety of methods, including, but not limitedto, brushing, roller coating, knife-over-roll, drawn-down using a bladecoater or spraying the solution on the surface.

If desired, the coating may be cured for a short time before use, e.g.at 160°-177° C. for from about 1 to about 4 minutes. Likewise, one mayif desired, employ a catalyst to assist in the curing. Examples ofsuitable catalysts include any of the well-known silicone curingcatalysts, such as, for example, benzoyl peroxide, dichlorobenzoylperoxide, and di-t-butyl peroxide and azo compounds, e.g.,azo-bis-isobutyronitrile; silanol-condensing catalysts, e.g., salts ofheavy metals, such as dibutyltin diacetate and stannous octoate;hydrosilation catalysts, e.g. platinum-containing catalysts, such achloroplatinic acid and platinum on charcoal; and lead, zinc or tinnaphthenates.

The amount of adhesive material which is applied to surfaces may bevaried to fit particular circumstances. Ordinarily, sufficient adhesiveshould be applied to render the surface definitely tacky to the touchafter the removal of any solvent. After applying it to the surface, theadhesive may be cured by air drying or by heating at temperaturesranging up to about 550° F. Heating will hasten removal of the solventand also tends to increase the cohesive strength of the adhesive film.After curing, the surfaces to be adhered are brought together. Nofurther curing is needed in order to establish a firm bond between thesurfaces.

Small amounts of additional ingredients can be added to the compositionsof the present invention if desired. For example, antioxidants,pigments, stabilizers, fillers and the like, can be added as long asthey do not materially deteriorate the pressure sensitive adhesiveproperties of the composition.

The compositions of the present invention are excellent pressuresensitive adhesives which also have excellent high temperaturestability. They will readily stick to a wide variety of supportsubstrates, whether flexible or rigid. Typically, useful supportsubstrates include, but are not limited to metals such as aluminum,silver, copper, iron and their alloys; porous materials such as paper,wood, leather, and fabrics; Kapton®, organic polymeric materials such aspolyolefins, such as polyethylene and polypropylene, fluorocarbonpolymers such as polytetrafluoroethylene and polyvinylfluoride, siliconeelastomers, silicone resins, polystyrene, polyamides such as nylon,polyesters and acrylic polymers; painted surfaces; siliceous materialssuch as concrete, bricks, cinderblocks and glass such as glass cloth,etc. These and other substrates, as known to those of ordinary skill inthe art, may be employed for use with the pressure sensitive adhesivesof the present invention.

It is further contemplated by the present invention that a primer beapplied to the substrate surface to prevent legging and webbingproblems. A primer which can be used in this invention is SS4191 primer,available from General Electric Company. The SS4191 primer is a toluenesolution of a curable dimethyl polysiloxane having a viscosity of10,000-18,000 centipoise at 25° C. The solids content of the primer isabout 29-31 percent. The SS4191 primer is normally used at a bathconcentration of 3-10 percent solids. The SS4191 primer can be used incombination with a catalyst, i.e., SS4192c catalyst, available fromGeneral Electric Company, and an accelerator, i.e. SS4259c accelerator,also available from General Electric Company. The SS4192c catalyst is a50% solution of dibutyl tin diacetate. The SS4259c accelerator is atoluene solution of methyl-2-methylaminoethoxy polysiloxanechain-stopped with trimethylsiloxy groups.

The SS4191 primer system contains 10 parts by weight of SS4191 primer,0.5 parts by weight of SS4192c catalyst, 0.5 parts by weight of SS4259caccelerator, 72 parts by weight of toluene and 18 parts by weight ofhexane. The system is prepared by diluting the SS4191 primer with thetoluene and hexane prior to the addition of the catalyst system andaccelerator. The ingredients are then mixed thoroughly. The primercomposition is applied to the substrate and cured for 30 seconds at 115°C.

It is noted that other primer compositions can be employed within thescope of the present invention.

The primer can be applied to the substrate by conventional methodswell-known in the art, e.g., spraying, roll coating, dip coating,brushing, and other art-recognized techniques.

Useful articles which can be prepared with the pressure sensitiveadhesives of the present invention include pressure-sensitive adhesivetapes, labels, emblems and other decorative or informative signs, etc.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples illustrate the present invention. They are not tobe construed to limit the scope of the appended claims in any mannerwhatsoever.

EXAMPLES 1 TO 3

About 300 parts per million of rare earth metals were incorporated intoeither of two silicone pressure sensitive adhesives, PSA-1 and PSA-2.

PSA-1 is a 55% solids in xylene silicone pressure sensitive adhesiveprepared by agitating a mixture of 51.3 parts MQ resin, 24.2 partsdimethylsiloxane gum, 24.5 parts xylene and 0.014 parts 10% NaOH inwater until a homogeneous solution is obtained. The mixture is thenheated to reflux and cooked at reflux for 2 hours. After the cookingstep, all of the water was trapped off, and the mixture was cooled. Thesolids content was then adjusted to 56% with xylene and the mixture wasneutralized to 0-15 ppm acid with 10% H₃ PO₄.

PSA-2 is a 60% solids in toluene silicone pressure sensitive adhesiveprepared by agitating a mixture of 40.6 parts MQ resin, 21.5 partsdimethylsiloxane gum, 14.3 parts toluene and 0.02 parts 10% NaOH inwater until a homogeneous solution is obtained. The mixture is thenheated to reflux and cooked at reflux for 2 hours. After the cookingstep, all of the after was trapped off, and the mixture was cooled. Thesolids content was then adjusted to 60% with toluene and the mixture wasneutralized to 0-15 ppm acid with 10% H₃ PO₄.

Rare earth octoate solution in hydrocarbon solvent, obtainedcommercially from Interstab (AKZO Chemmie), is added to the respectivesilicone composition. The composition was then coated on a 1 milpolyimide film which was primed with SS4191 primer system (GeneralElectric Company) to about 1.5 to 2 mils. The adhesive was cured for 3minutes at 175° C., after a 30 second solvent flashing. Peel adhesionagainst steel plate and probe tack adhesion were measured. The elevatedtemperature stability was investigated by exposing the cured adhesive ina 550° F. air circulating furnace for 72 hours. The exposed tapes wereexamined for delamination from backing, cracking and edge curling.

The metal stabilizer is varied in additional examples. The results,along with compositional data, are set forth below in Table 1.

                  TABLE 1                                                         ______________________________________                                                   Example                                                                       1      1A*    2        2A*  3                                      ______________________________________                                        Composition                                                                   PSA-1.sup.a  X        X      --     --   --                                   PSA-2.sup.b  --       --     X      X    X                                    Rare Earth.sup.c, ppm                                                                      300      50     300    50   --                                   Cerium.sup.d --       --     --     --   300                                  Properties                                                                    Peel oz/in    27      28      28    28    30                                  Tack, g/cm.sup.2                                                                           482      548    662    688  658                                  550° F. aging                                                                       Pass     Fail   Pass   Fail Pass                                 ______________________________________                                         * = Comparative Example                                                       .sup.a = Silicone Pressure Sensitive Adhesive                                 .sup.b = Silicone Pressure Sensitive Adhesive                                 .sup.c = Rare earth metals in hydrocarbon solvent from Interstab (AKZO        Chemmie)                                                                      .sup.d = Cerium metal salt from Mooney Chemical Company                  

As can be seen from Table 1 above, silicone pressure sensitive adhesivescomprising the metal stabilizers in accordance with the appended claimsexhibit improved high temperature stability over the silicone pressuresensitive adhesives of the prior art.

EXAMPLES 4 TO 5

The procedure of Example 1 is followed except that the effectiveness ofother metals, in the form of metal carboxylate salts are tested. Theadhesives are further incorporated with 0.55 g of benzoyl peroxidecuring agent. The results, along with compositional data, are set forthbelow in Table 2.

                  TABLE 2                                                         ______________________________________                                                    Example                                                                       4    4A*       5      5A*                                         ______________________________________                                        Composition                                                                   PSA-1.sup.a, gm                                                                              50    50         50   50                                       Magnesium, ppm                                                                              .sup. 300.sup.b                                                                      --        --   .sub. 110.sup.c                           Zinc.sup.d, ppm                                                                             360    --        --   --                                        Zirconium.sup.e, ppm                                                                        --     --        300  --                                        Properties                                                                    Peel, oz/in   30     29         30   30                                       Tack, g/cm.sup.2                                                                            750    644       620  748                                       550° F. aging                                                                        Pass   Fail      Pass Fail                                      ______________________________________                                         * = Comparative Example                                                       .sup.a = Silicone Pressure Sensitive Adhesive                                 .sup.b = 0.42 g of 2% Magnesium TenCem, Mooney Chemical Company               .sup.c = 0.155 g of 2% Magnesium TenCem, Mooney Chemical Company              .sup.d = 0.124 g of 8% Zinc HexCem, Mooney Chemical Company                   .sup.e = 0.137 g of 6% Zirconium HexCem, Mooney Chemical Company         

EXAMPLES 6 TO 10

The procedures of Examples 1-5 were followed to test various metalstabilizing systems. The adhesives were further incorporated with 0.55 gof benzoyl peroxide. The adhesive films were prepared as described inExample 1 and cured for 3 hours at 200° C., after a 90 second flash at70° C. The cured films were then tested for heat stability for 72 hoursat 550° F. The results, along with compositional data, are set forthbelow in Table 3.

                  TABLE 3                                                         ______________________________________                                                    Example                                                                       6     7       8       9     10                                    ______________________________________                                        Composition                                                                   PSA-1.sup.a, gm                                                                              50      50      50    50    50                                 Cerium, ppm   160.sup.b                                                                             160.sup.b                                                                             160.sup.b                                                                           240.sup.c                                                                           286.sup.d                           Magnesium, ppm                                                                               60.sup.e                                                                             --      100.sup.f                                                                           --    --                                  Zinc, ppm     --      100.sup.g                                                                             --    160.sup.h                                                                           114.sup.i                           Properties                                                                    550° F. aging                                                                        Pass    Pass    Pass  Pass  Pass                                ______________________________________                                         .sup.a = Silicone Pressure Sensitive Adhesive                                 .sup.b = 0.075 g of 6% Cerium HexCem, Mooney Chemical Company                 .sup.c = 0.110 g of 6% Cerium HexCem, Mooney Chemical Company                 .sup.d = 0.130 g of 6% Cerium HexCem, Mooney Chemical Company                 .sup.e = 0.078 g of 2% Magnesium TenCem, Mooney Chemical Company              .sup.f = 0.138 g of 2% Magnesium TenCem, Mooney Chemical Company              .sup.g = 0.0344 g of 8% Zinc HexCem, Mooney Chemical Company                  .sup.h = 0.055 g of 8% Zinc HexCem, Mooney Chemical Company                   .sup.i = 0.0392 g of 8% Zinc HexCem, Mooney Chemical Company             

Table 3 above demonstrates that combinations of other metal salts withcerium metal salts provide improved high temperature stabilityadhesives.

EXAMPLES 11 TO 12

The use of the metal salts to improve elevated temperature stability wasfurther tested in silicone pressure sensitive adhesives based onplatinum-catalyzed addition cure of a high solids vinyl- andmethylhydrogen-containing silicones. The compositions contain twocomponents, PSA-Vi and PSA-MeH.

The PSA-Vi component is a silicone pressure sensitive adhesivecontaining 94% solids in 6% toluene. The adhesive composition solidscomprise 58% of an MQ resin and 52% of a vinyl terminated fluidcontaining 105 D units, The composition further comprises 60 ppmplatinum catalyst.

The PSA-MeH component is also a silicone pressure sensitive adhesivecomposition containing 94% solids in 6% toluene. The adhesivecomposition solids comprise 58% of MQ resin and 42% of a mixturecontaining 80 mol % hydride terminate fluid containing 121 D units and20 mol % of a hydride crosslinker having an HEW (hydrogen equivalentweight) of 625.

The components are then further mixed with a crosslinker having thegeneral formula MD₂₀ D^(H) ₃ M having an HEW of 625.

The appropriate metals are added to the adhesive and the adhesivecomposition is then coated over an SS4331 primed (A silicone primersystem, available from General Electric Company, containing 13.3 partsof SS4331 polydimethylsiloxane solution, 0.25 parts of SS8010platinum-containing catalyst solution, 0.14 parts of SS4300Cmethylhydrogen silicone crosslinker, and 76 parts of hexane solvent) 1mil polyimide film and cured 3 minutes at 150° C. for high temperatureexposure. The adhesive properties are reported on 1 mil polyester filmbacking. The results, along with composition data are set forth below inTable 4.

                  TABLE 4                                                         ______________________________________                                                      Examples                                                                      11      11A*      12                                            ______________________________________                                        Composition                                                                   PSA-Vi.sup.a     10        10        10                                       PSA-MeH.sup.b    9.51      9.51      9.51                                     Crosslinker.sup.c                                                                              0.18      0.18      0.18                                     Stabilizer, ppm 300.sup.d  50.sup.e 300.sup.f                                 Properties                                                                    Peel oz/in       25        30        26                                       Tack, g/cm.sup.2                                                                              642       642       658                                       550° F. aging                                                                          Pass      Fail      Pass                                      ______________________________________                                         * = Comparative Example                                                       .sup.a = Silicone Pressure Sensitive Adhesive                                 .sup.b = Silicone Pressure Sensitive Adhesive                                 .sup.c = MD.sub.20 D.sup.H .sub.3 M crosslinker                               .sup.d = 0.0585 g of 6% rare earth octoate, Interstab (AKZO Chemmie)          .sup.e = 0.0152 g of 6% rare earth octoate, Interstab (AKZO Chemmie)          .sup.f = 0.0585 g of 6% cerium HexCem, Mooney Chemical Company           

Table 4 above demonstrates that adhesives exhibiting improved hightemperature stability can be prepared from adhesives containing highsolids vinyl and hydrogen stopped fluids.

The above-mentioned patents are hereby incorporated by reference.

Many variations of the present invention will suggest themselves tothose of ordinary skill in the art in light of the above-detaileddescription. All such obvious modifications are within the full intendedscope of the appended claims.

We claim:
 1. A silicone pressure sensitive adhesive having improved hightemperature stability comprising:(a) an aromatic hydrocarbon solubleresin copolymer comprising R₃ SiO_(1/2) units and SiO_(4/2) units whereeach R individually represents a monovalent hydrocarbon radicalcontaining no more than six carbon atoms where the total number of Rradicals having olefinic unsaturation is between 0 and 0.25 percent,there being from about 0.6 to about 0.9 R₃ SiO_(1/2) units for everySiO_(4/2) unit; (b) a hydroxyl, vinyl or hydride end-stoppeddiorganopolysiloxane and (c) from about 200 to about 500 parts permillion metal of oil- or organic-soluble metal salts based on the totalsilicone weight of (a) and (b).
 2. A silicone pressure sensitiveadhesive as defined in claim 1 wherein component (a) is present in anamount ranging from about 80 to about 40 parts by weight and component(b) is present in an amount ranging from about 20 to about 60 parts byweight based on 100 parts by weight of (a) and (b) together.
 3. Asilicone pressure sensitive adhesive as defined in claim 2 whereincomponent (a) is present in an amount ranging from 80 to about 50 partsby weight and component (b) is present in an amount ranging from about20 to about 50 parts by weight based on 100 parts by weight of (a) and(b) together.
 4. A silicone pressure sensitive adhesive as defined inclaim 1 wherein said component (b) comprises a hydroxyl end-stoppeddiorganopolysiloxane of the general formula: ##STR2## wherein each R¹individually is a radical selected from the group consisting of alkylradicals, alkenyl radicals, cyclic hydrocarbon radicals and arylradicals wherein x is a number sufficient to provide a viscosity of fromabout 100,000 to 500,000,000 centipoise at 25° C.
 5. A silicone pressuresensitive adhesive as defined in claim 4 wherein each said R¹ isindependently selected from the group consisting of methyl, ethyl,propyl, hexyl, octyl, vinyl, allyl, propenyl, butenyl, hexenyl,cyclohexyl, cyclohexenyl, phenyl, 2-phenylethyl, tolyl and benzyl.
 6. Asilicone pressure sensitive adhesive as defined in claim 5 wherein atleast 95 percent of the organic radicals in components (a) and (b), Rand R¹ are methyl.
 7. A silicone pressure sensitive adhesive as definedin claim 6 wherein all of the organic radicals in components (a) and (b)are methyl.
 8. A silicone pressure sensitive adhesive as defined inclaim 7 wherein said hydroxyl end-stopped organopolysiloxane component(b) comprises silanol-stopped polydimethylsiloxanes.
 9. A siliconepressure sensitive adhesive as defined in claim 1 wherein said component(b) comprises a mixture of vinyl and hydride end-stoppedorganopolysiloxane fluids.
 10. A silicone pressure sensitive adhesive asdefined in claim 1 wherein said component (c) is present in an amountranging from 200 parts per million metal to 2500 parts per million metalbased on total silicone weight.
 11. A silicone pressure sensitiveadhesive as defined in claim 1 wherein said oil or organic soluble metalsalt comprises a metal salt of a carboxylic acid having from about 2 toabout 18 carbon atoms.
 12. A silicone pressure sensitive adhesive asdefined in claim 1 wherein the metal is selected from rare earth metalsselected from lanthanum, cerium, praesodymium, neodymium, promethium,samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium,thulium, ytterbium and lutetium.
 13. A silicone pressure sensitiveadhesive as defined in claim 1 wherein the metal comprises a transitionmetal.
 14. A silicone pressure sensitive adhesive as defined in claim 13wherein said transition metal is selected from the group consisting ofzirconium, titanium, nickel, iron, vanadium, chromium, maganese, cobaltand copper.
 15. A silicone pressure sensitive adhesive as defined inclaim 1 wherein the metal is selected from the group consisting ofmagnesium, calcium, barium, aluminum and tin.
 16. A silicone pressuresensitive adhesive as defined in claim 12 wherein said oil or organicsoluble metal salt comprises a rare earth metal 2-ethylhexanoate, rareearth metal octoate or a mixture thereof.
 17. A silicone pressuresensitive adhesive as defined in claim 12 wherein said oil- ororganic-soluble metal salt comprises cerium 2-ethylhexanoate, ceriumoctoate or a mixture thereof.
 18. An improved silicone pressure adhesivehaving improved high temperature stability comprising:(a) an aromaticsoluble resin copolymer comprising R₃ SiO_(1/2) units and SiO_(4/2)units where each R individually represents a monovalent hydrocarbonradical containing no more than six carbon atoms, there being from about0.6 to about 0.9 R₃ SiO_(1/2) units for every SiO_(4/2) unit; (b) ahydroxyl, vinyl or hydride end-stopped diorganopolysiloxane; theimprovement comprising:adding (c) from about 200 to about 500 parts permillion metal of oil or organic soluble metal salts based on the totalsilicone weight of (a) and (b).
 19. A silicone pressure sensitiveadhesive as defined in claim 18 wherein said oil or organic solublemetal salt comprises a metal salt of a carboxylic acid having from about2 to about 18 carbon atoms.
 20. A silicone pressure sensitive adhesiveas defined in claim 19 wherein said oil or organic soluble metal saltcomprises a rare earth metal octoate, a rare earth metal2-ethylhexanoate or a mixture thereof.
 21. A silicone pressure sensitiveadhesive as defined in claim 20 wherein said oil or organic solublemetal salt comprises cerium 2-ethylhexanoate, cerium octoate or amixture thereof.
 22. A method for improving the high temperaturestability of a silicone pressure adhesive comprising (i) adding to asilicone pressure adhesive comprising (a) a benzene soluble resincopolymer comprising R₃ SiO_(1/2) units and SiO_(4/2) units where each Rindividually represents a monovalent hydrocarbon radical containing nomore than six carbon atoms, there being from about 0.6 to about 0.9 R₃SiO_(1/2) units for every SiO_(4/2) unit; and (b) a hydroxyl, vinyl orhydride end-stopped diorganopolysiloxane; (ii) from about 200 to about500 parts per million metal of (c) oil- or organic-soluble metal saltsbased on the total silicone weight of (a) and (b).
 23. A siliconepressure sensitive adhesive as defined in claim 22 wherein saidcomponent (c) is present in an amount ranging from 200 parts per millionmetal to 2500 parts per million metal based on total silicone weight.24. A silicone pressure sensitive adhesive as defined in claim 22wherein said oil or organic soluble metal salt comprises a metal salt ofa carboxylic acid having from about 2 to about 18 carbon atoms.
 25. Asilicone pressure sensitive adhesive as defined in claim 24 wherein saidoil or organic soluble metal salt comprises a rare earth metal octoate,a rare earth metal 2-ethylhexanoate or mixtures thereof.
 26. A siliconepressure sensitive adhesive as defined in claim 21 wherein said oil ororganic soluble metal salt comprises cerium 2-ethylhexanoate, ceriumoctoate, or mixtures thereof.